1. Field of the Invention
This invention relates to a development in the production of dyes and, more particularly, to a development in the production of dustless FD&C dyes of high tinctorial character.
2. Description of the Related Art
The use of coloring agents in imparting or modifying the color of textiles, materials and foods dates back many thousands of years. These agents have come to be known as "dyes." Dye extracts have been obtained from both animals and plants. For example, cochineal is a bright red dye which, for centuries, has been extracted from the female Coccus cacti species of beetles indigenous to Central and South America and Mexico. Other dyes, such as indigo or "royal blue" which many regard as the world's oldest and most highly coveted dye, derive from plant life commonly found in India and South America.
The safety of dyes, particularly as used in foods, came into critical focus beginning in the early nineteenth century. It was at this time in history when foods such as pickles were colored with poisonous copper sulfate and candy was colored with toxic salts of lead and copper. In addition, a desirably darker color was commonly being imparted to tea leaves using deleterious lead-based compounds.
Synthetic creation of dyes led to the development of stronger and more stable dye compositions. Beginning in 1886, the United States began formulating policy governing the manufacture of dyes intended for use in foods. Subsequent legislation followed in 1907, 1938 and most recently in 1960 with the enactment of the Color Additive Amendment.
A component of this law required that long-term chronic feeding studies be conducted in at least two animal species. Further, the United States Food and Drug Administration (FDA) ordered dye manufacturers to submit representative samples of their products for evaluation. Based upon the results of these tests, the FDA formulated dye manufacturing standards and specifications and permanently approved for use in foods, drugs and cosmetics the following seven dyes: Red 40; Yellow 5; Yellow 6; Blue 1; Blue 2; Red 3; and Green 3. Dyes that comply with such standards and specifications are known as FD&C dyes.
To ensure compliance with the specifications so formulated, the FDA now requires FD&C dye manufacturers to submit for laboratory evaluation a 4 ounce sample from every batch of food dye produced. It is unlawful to sell any fraction of the batch prior to receiving FDA approval.
Synthetic dyes are both produced and most commonly used in solution form. Despite this, however, they generally pass as staple articles of commerce in dry powder form. The batch samples forwarded for approval to the FDA must also be submitted in dry powder form.
The use of FD&C dyes in food products, while commercially practical and feasible, can be readily characterized as a messy operation. In fact, during transportation, handling and use, it is invariable that microparticulate dye powders disperse in the vicinity of the operation. Airborne color dust is also very common and has a very high potential for cross-contaminating the other products of the user as well as his/her offices, warehouses and related operations facilities. Thus, efforts have been made in the art to develop less dusty dyes in order to prevent product cross-contamination and to reduce the time and expense incident to clean-up.
The prevailing industry trend toward developing a less dusty dye powder has been in the direction of granulation. Until now, however, granulation development has been largely unsuccessful due to the inability to make a substantially dustless and abrasion-resistant granular dye that dissolves readily when intended for use.
Following chemical synthesis of a dye, the solution must be dried and further processed to form a granular powder product. Accordingly, the dustiness of the finished product bears relation to both the method of drying and the granulation process. Three methods are known for drying FD&C dye solutions to produce granular powders. They are tray drying, spray drying followed by compaction milling and agglomeration followed by fluid bed drying.
Tray drying is, perhaps, the oldest known method of drying FD&C color solutions. In accordance with this method, a purified filter cake or concentrated color solution is first obtained by filtration of the chemically synthesized dye solution. The cake or solution is then placed in a shallow tray and dried in a conventional walk-in oven for approximately 48 hours at a temperature of 200.degree.-250.degree. F. Thereafter, a hard, dry cake is recovered from the oven and subjected to a grinding and screening/sifting operation. Coarse particles must be re-ground while fine particles are sold as powder and mid-sized particles are sold as granules. Tray drying fails to produce a desirable granular dye. Rather, a substantial component of the product yield is in the form of powdery dust that cannot be cost-effectively converted to granules. Further, even the granular product that can be produced is substantially prone to disintegration through abrasion. The result is that tray-dried product that is packaged for shipment in the form of granules often reaches its destination in the form of a powdery dust that is difficult to use without significant risk of cross-product contamination and substantial clean-up implications. Tray drying is also economically unattractive due to the labor intensity of the method.
Among the most cost-effective methods of drying purified concentrated color solutions is spray drying. Because the product generated by this procedure tends to be very dusty, however, it is not suitable for many applications. In the spray-drying procedure, a compaction mill is commonly used to granulate the spray-dried color. The color composition is fed between two closely spaced high pressure rollers which physically press the powder into a sheet. The sheet composition is then subjected to grinding and sifting/screening. Fine and coarse particles are recycled back through the mill. The mid-sized particles are sold as granules. It is common that as much as 40% of the material must be recycled in order to obtain sufficient amounts of desirable granular product. Furthermore, like the tray-dried granular product, the granular product obtained by this process is also highly vulnerable to the effects of abrasion which results in the very dust and disintegration problems that granules are intended to overcome. Blended granular dyes are also difficult to produce cost-effectively in small volumes by this method.
Agglomeration coupled with fluid bed drying is yet another known drying process. In contrast to the other methods thus discussed, fluid bed drying utilizes a dry dye composition rather than a solution composition as a starting material. The process involves mixing the dry dye with concentrated color solution in a high speed mixer. The result is that enlarged or swollen wetted particles (i.e. agglomerates) are formed which are then subjected to fluid bed drying. Once dried, the particles are screened with the fine and coarse particles being recycled back again through the process. The mid-sized particles are recovered and sold as granular dyes. Like the other known drying methods, agglomeration drying produces granular dye products that readily abrade and disintegrate during handling and shipment thereby causing significant powder dust problems. Also, sufficient granular production by this method involves the recycle of up to 50% of the product. Furthermore, agglomeration drying is not feasible for manufacturing blended dyes in small volumes.
Thus, the art has lacked an effective and convenient method for treating liquid solutions of chemically synthesized FD&C dyes to produce an abrasion resistant, substantially dust-free granular dye that dissolves readily when intended for use. The invention disclosed and claimed herein achieves these advantages in a manner not revealed by the prior art.